Method and apparatus for coin selection utilizing inductive sensors

ABSTRACT

The method and apparatus of this invention examine properties of coins by subjecting them to electromagnetic fields of at least two substantially different frequencies. An indication that a coin is acceptable is produced only after the coin has satisfied the examination requirements at at least two substantially different frequencies.

United States Patent [191 Fougere Mar. 11, 1975 METHOD AND APPARATUS FOR COIN SELECTION UTILIZING INDUCTIVE SENSORS [75] lnventor:

[73] Assignee: Arthur D. Little, Inc., Cambridge,

Mass.

22 Filed: on. 12, 1973 211 Appl. Not: 405,881

Related US. Application Data [63] Continuation of Ser. No. 255,814, May 22, 1972,

Guy L. Fougere, Lincoln, Mass.

abandoned.

[30] Foreign Application Priority Data Feb. 25, 1972 Great Britain 8385/72 52 us. Cl 194/100 A [51] Int. Cl. G07f 3/02 [58] Field of Search 194/100, 100 A, 99, 101,

[56] References Cited UNITED STATES PATENTS 3,059,749 10/1962 Zinke 194/100 3,599,771 8/1971 Hinterstocker..... 194/100 A Primary ExaminerStanley H. Tollberg Attorney, Agent, or FirmDavis, Hoxie, Faithful] & Hapgood [57] ABSTRACT The method and apparatus of this invention examine propertiesof coins by subjecting them to electromagnetic fields of at least two substantially different frequencies. An indication that a coin is acceptable is produced only after the coin has satisfied the examination requirements at at least two substantially different frequencies.

60 Claims, 13 Drawing Figures PATENTED R 1 i575 3,870,137

FIG. 8 M

PATENIED 1 I975 sum 5 or 5 Flcjn METHOD AND APPARATUS FOR COIN SELECTION UTILIZING INDUCTIVE SENSORS This application is a continuation of application Ser.

No. 225,814, filed May 22, 1972 now abandoned.

The method and apparatus of this invention examine the material properties of coins by subjecting them to electromagnetic fields of at least two substantially different frequencies. A determination is made for each of the examination frequencies whether or not the interaction between the coin being tested and the electromagnetic field of that frequency produces the interaction effect within predetermined tolerances which is anticipated for acceptable electrically conductive coins. Certain of the examinations can be made in such a manner that the resulting signal is also indicative of whether the coin is within certain ranges of coin diameter and thickness. The coin selector produces an indication that a coin is acceptable only after the coin has satisfied the examination requirements at at least two substantially different frequencies.

No moving parts are required in this coin selector, except a device to separate acceptable coins from nonacceptable coins in accordance with the indication of acceptability and except as mechanical energy absorbing elements may be characterized as moving parts.

Throughout this specification the term coinf is intended to mean genuine coins, tokens, counterfeit coins, slugs, washers, and any other item which may be used by persons in an attempt to use coin-operated devices/Furthermore, throughout this specification, for simplicity, coin movement is described as rotational motion; however, except where otherwise indicated, translational motion also is contemplated.

In the drawings:

FIG. I is a front elevational drawing of the coin track and inductors of a coin selector formed in accordance with this invention.

FIG. 2 is an end view of the coin selector of FIG. 1

'- at section AA.

FIG. 3 is a simplified front elevational drawing of details of an alternative arrangement of a coin track and inductors for a coin selector formed in accordance with this invention.

FIG. 4 is a schematic block diagram of the electronic circuit for a coin selector formed in accordance with this invention.

FIG. 5 is the top view of a typical pot core inductor.

FIG. 6 is a cross-sectional view along line AA of the pot core inductor of FIG. 5.

FIG. 7 is a schematic block diagram of an alternative low frequency sub-circuit for a coin selector formed in accordance with this invention.

FIG. 8 is a schematic block diagram of a digital electronic circuit for a coin selector formed in accordance with this invention.

FIG. 9 is a schematic block diagram of a coin selector in accordance with this invention.

FIG. 10 is a schematic diagram of a high frequency oscillator and detectors for the coin selector of FIG. 9.

FIG. 11 is a schematic diagram ofa low frequency oscillator, bridge and detector for the coin selector of FIG. 9.

FIG. 12 is a schematic block diagram of a further coin selector formed in accordance with this invention.

FIG. 13 is a schematic block diagram of a portion of another coin selector in accordance with this invention.

The figures are intended to be representational and are not necessarily drawn to scale.

According to the method of this invention, a coin being examined is subjected to electromagnetic fields of at least two substantially different frequencies which have been selected as appropriate for the examination of the set of coin denominations which are to be accepted by the apparatus employing the method. The lower frequency (LF) is one which, when applied to an appropriate electromagnetic radiator or inductor, will penetrate deeply into or through the coins of acceptable denominations.

The higher frequency (HF) is one which will penetrate not more than halfway through the thickness of the most worn coin to be accepted of all acceptable denominations. In most instances the system is designed so the HF penetrates into a small percentage of the coins thickness. In. the case where laminated coins, such as the present IO-cent, 25-cent and 50-cent denomination coins of the United States of America, are to be examined; an appropriate high frequency would be one which will penetrate to approximately the thickness of the outer layer or cladding of coins of the denomination having the thinnest outer layer.

For the purpose of this discussion, the depth of penetration or skin depth d in centimeters is defined as:

k is a constant having a value dependent upon the system of measurement, where,fis the frequency, a is the DC conductivity and ,u is magnetic permeability of the material. At this depth, the current density is 36.8 percent of the current density at the surface of the material. For copper, for example, this formula indicates that the skin depthis 6.62/ Vffior 0.00662 cm. at 1 MHz, 0.0208 cm. at 100 kHz, 0.0662 cm at 10 kHz and 0.208 cm. at 1 kHz. For an alloy of percent cooper 25 percent nickel, which is used for the outer lamina of the US. 10 cent and 25 cent coins and has a substantially lower conductivity than copper, the skin depth is 0.029 cm. at 1 MHz, 0.091 cm. at kHz, 0.29 cm. at 10 kHz and 0.91 cm. at l.kI-Iz.

When a ferromagneticcoin shunts an inductor, such as the pot core inductor 200 shown in FIGS. 5 and 6, in an alternating current cirucit; the direction of change of inductance of the inductor depends on both the skin effect and the effect of shunting by the magnetic material. Thus, if the magnetic permeability of a coin is high and the conductivity is low, the inductance of the inductor will increase. If the permeability is low and the conductivity is high, the inductance will decrease. Both types of inductance change can be utilized in the method and apparatus of this invention.

When a nonmagnetic coin shunts the inductor, the magnetic flux flowing through the coin material induces currents which produce an opposing field. This tends to prevent the flux from penetrating far into a coin of high conductivity; for coins of lower conductivity the flux can penetrate further as discussed above. The inductance of the inductor coil will be altered, but for discs of different metals of the same diameters and equal thicknesses as measured in skin depths the inductance change will be different. Naturally when the thickness of the discs becomes small relative to one skin depth, the difference tends to disappear. The method of the invention provides a powerful means of coin discrimination by examining each coin in this fashion at two substantially different frequencies, a lower frequency at which the coin thickness is relatively small in terms of penetration of the flux and a higher frequency at which only shallow penetration occurs, and accepting the coin only if it satisfies the criteria for a genuine coin of the same denomination on both tests.

Depending upon the set of coin denominations to be accepted by a coin selector, a selection of the lower and higher frequencies to be employed can be made; taking into consideration the relative positions of the inductors and the coins when the coins are being examined. A final selection of inductor positions and frequencies can then be made following tests of a prototype unit. Generally, there is a large ratio between the low frequency and the high frequency, for example, LF between 5 and 25 kHz and HF between 200 and 800 kHz are the approximate preferred ranges for a coin set consisting of the US. S-cent, IO-cent and 25-cent denomination coins. When all of the coins in a set are of a low conductivity material, a maximum LP of approximately 60 kHz and a minimum HF of approximately 100 kHz could be used; a frequency ratio of approximately 1.6 to 1. As a general proposition, while there may be exceptions in some cases, the LF will be in the vicinity of 60 kHz or less and the HF will be in the vicinity of 100 kHz or more, the dividing line being approximately 75 kHz.

Practical consideration suggest that frequencies between approximately 3 kHz and lMHz be used in most cases. At frequencies lower than about 3 kHz, the flux fully penetrates all but the thickest coins of the highest conductivity and it becomes increasingly difficult to subject a rapidly moving coin to the electromagnetic field for a sufficient period to accurately and economically detect the interaction between coin and field. At frequencies in the vicinity of 1 MHz and above for coins of higher conductivity material, where the peaks of the surface of the coin being tested are at a very short fixed distance from the inductor, the method will be sensitive to the embossing on the surface of the coin. This may be objectionable in some cases, however, such frequencies may be employed to distinguish between the sides. (heads or tails) of genuine coins, to distinguish between genuine coins which are embossed and unembossed slugs of the same material, or even to distinguish between otherwise similar coins of different nations which are differently embossed. At somewhat greater distances from the coin to inductor, these frequencies tend to produce results indicative primarily of the distance of spacing of the coin from the inductor.

FIRST EMBODIMENT A coin selector formed in accordance with the present invention is shown in the drawings. A coin may be introduced into the coin selector 10 through the coin entry 20. The coin then falls under the influence of gravity onto the coin track 30. The main portion 31 of the coin track 30 is sloped downwards in a direction away from the coin entry 20. The portion of the coin track 30 onto which the coin initially falls may be merely an upward extension at the same angle of slope as the main portion 31, as indicated in FIG. 1; but preferably the initial portion 32 is at a steeper angle than the main portion 31. One advantageous form of the initial portion 32, which is shown in FIG. 3, is for the initial portion 32 of the coin track 30 to be curved upwards from the main portion 31 beneath the coin entry 20, so that the vertical motion of a coin entering the coin selector 10' through the coin entry 20 under the influence of gravity will be transformed into motion along the main portion 31 of the coin track 30 with a minimum of coin bouncing. Coin tracks 30 having slopes at an angle from the horizontal of from 10 to 25 have been found to be satisfactory.

Adjacent and contiguous to the coin track 30 is a sidewall 40 which is canted at a sufficient angle from the vertical to cause the face of a coin to bear against the wall 40, when the edge of the coin is resting on the coin track 30. An angle of 20 from the vertical has been found to be a satisfactory angle for the sidewall 40. The coin track 30 is ordinarily arranged at a right angle to the sidewall 40 and spaced away from sidewall 40 by a distance greater than the thickness of the thickest coin which is to be selected by the coin selector 10. The coin track 30 and the sidewalls 40 and 50 form a coin passageway 60. The sidewall 40 and the coin track 30 may conveniently be molded from the same piece of material.

In a coin selector 10, which is designed to examine and accept genuine coins of three different denominations, a set of four inductors 72, 74, 76 and 78, are located along one side of the. coin passageway 60. Each of the inductors 72, 74, 76 and 78 is similar to the typi-' cal inductor 200 shown in FIGS. 5 and 6. Inductor 200 comprises a coil 201 wound on a bobbin 202, which is placed around the center pole 204 of a ferrite pot core 203. One of the set of inductors 70, inductor 72 in the coin selector 10, is designed for operation in an oscillator circuit at a relatively low frequency. The remaining inductors in the set 70, inductors 74, 76 and 78 of the coin selector 10, are designed for operation in oscillator circuits at substantially higher frequencies than that of inductor 72.

Each of the inductors of set 70 is placed in the sidewall 40 with their pole faces toward the coin passageway 60, and with gap corresponding to gap 205 of the typical inductor 200, running in a direction perpendicular to the coin track 30. The pole faces of each inductor, corresponding to the faces of poles 204, 206 and 207 of the typical inductor 200, are separated from the coin passageway by an approximately ten-thousandths of an inch of epoxy impregnated fiberglass which forms the inner surface 42 of sidewall 40. The smooth inner surface 42 of the sidewall 40 promotes rapid travel of coins through the coin selector 10.

Inductors 72 and 74 are located at a distance from the coin track 30 such that the smallest coin which the coin selector is to accept, the lO-cent piece in the case of coin selector 10, will be concentric with the inductor when placed adjacent the inductor on the coin track 30. Similarly, the inductors 76 and 78 are placed at a distance from the coin track 30 such that the successively larger coins to be examined by the coin selector, the 5-cent and 25-cent pieces in the case of coin selector 10, are concentric with the respective inductors when they are adjacent the inductor and on the coin track 30.

The inductor 72 is part of the resonant circuit of an electronic oscillator 80. One such oscillator has been constructed which has an idling frequency of 9.3 kHz. when there is no electrically conductive material in the vicinity of the pole faces of the inductor 72. When nonmagnetic electrically conductive material is placed in the vicinity of the pole faces corresponding to the faces of poles 204, 206 and 207 of the typical inductor 200, however, the oscillation frequency is increased. In the case of the S-cent, -cent and -cent pieces, respectively, the peak frequency reached as the coin rolls past inductor 72 on the coin track were approximately 10.67 kHz., 11.87 kHz. and 12.18 kHz. The peak frequency is dependent upon the conductivity of the coin, as well as the permeability and thickness of the coin (in some cases) and percentage of magnetic flux from the inductor 72 which is shunted by the coin a function primarily of the sizes and relative locations of the coin and the inductor 72.-

A narrow-band detector circuit 81 having a center frequency of 10.67 kHz. is arranged to monitor the oscillator frequency. When a coin is rolled past inductor 72, the'detector will produce a single output signal when the frequency reaches approximately 10.67 kHz;

however, when a lO-cent or 25-cent piece rolls past the inductor the oscillator frequency will go through 10.67 kHz to a higher frequency and through again when the frequency decreases as the coin approaches inductor 72 and then goes away from inductor 72. As a result, the narrow'band detector 81 will produce two output signals in the case of the lO-cent and 25-cent pieces passing inductor 72. A second narrow-detector 82, arranged to indicate the presence of signals of the frequencies in the range from ll.87 through l2.l8 kHz., would produce no useful output signal when a 5-cent piece passed inductor 72, as the. oscillator frequency would never reach ll.87 kHz., but would produce a single output signal when a lO-cent or 25-cent piece passed that inductor.

Many kinds of slugs and non-acceptable coinage differ substantially in low frequency conductivity from genuine 5, l0 and 25-cent pieces. When such pieces pass inductor 72 either two signals or no signal will be produced at the output of each of these detectors 81 and 82. The coin selector 10 can distinguish a genuine 5-cent piece from genuine l0 and 25-cent pieces and from many kinds of slugs and non-acceptable coinage by accepting only coins which produce a single output from one of the detectors 81 and 82 and rejecting coins which produce either no output or two outputs from each detector 81 and 82.

Each of inductors 74, 76 and 78 is connected in the resonant circuit of an oscillator circuit 84, 86 and 88 respectively, which is designed to reach a maximum frequency of 455 kHz. when a lO-cent, 5-cent or 25- cent piece passes its associated inductor 74, 76 or 78 respectively. Each of the oscillator circuits 84, 86 and 88 may have a different idling frequency in the absence of coins, usually somewhere in the range of 300-400 kHz. For example, the idling frequencies of oscillator circuits 84, 86 and 88 in an experimental coin selector were 349, 345 and 344 kHz. respectively.

The frequencies generated by each of the oscillators 84, 86 and 88, associated with inductor 74, 76 and 78 are monitored by three narrow-band detector circuits 85, 87 and 89 respectively. Each of the detector circuits has a 455 kHz. ceramic filter, for example Murata type SF-455-D distributed by The Murata Corp. of America, New York, New York. Such filters, which are now commonly used in radio receivers, are readily available and inexpensive. As in the case of inductor 72, a determination can be made of whether a genuine coin has passed one of inductors 74, 76 or 78, by determining whether the associated detector, 85, 87 or 89 has produced one output pulse, two output pulses or none. A single output pulse from one of the detectors would indicate that a conductive object which has passed the associated inductor has caused the oscillator frequency to shift from the idling frequency to 455 kHz. and then return toward the idling frequency, denoting the possibility of a genuine coin of the denomination associated with that inductor. No output pulse from a given detector would indicate that either no conductive object has passed the associated inductor, or that the conductivity and permeability of an object that has passed the inductor, and location of the object with respect to the inductor (a function of object diameter, and inductor diameter and height above the track) was such that the frequency was not shifted from the idling frequency to 455 kHz. Two output pulses from the detector would indicate that the frequency was shifted beyond 455 kHz., beyond the narrow bandwidth of the detector, and then returned to the idling frequency; which is also an indication that the object passing the inductor is not a genuine coin of the associated denomination.

Three AND-gates 101, 102 and 103 are arranged to provide a signal indicative of whether a coin being examined has produced an indication of potential acceptability at both a low frequency and a high frequency. The first AND gate 101 is connected to the output of flip-flop 91. A signal on this output indicates that a coin is potentially a lO-cent or 25-cent piece. The other input of gate 101 is connected to flip-flop 94 which provides an indication of whether the coin being examined has satisfied the high frequency test for a 10-cent piece. The second AND gate 102 is connected to the output of flip-flop 91 and to flip-flop 98, each of which provides indications of whether a coin is potentially a 25-cent piece. The third AND gate 103 is connected to the output of flip-flop 92 and to the output of flip-flop 96, which each provide an indication of whether a coin is potentially a S-centpiece. When both of the inputs of one of the AND gates 101, 102 or 103 receive a positive indication, that AND gate produces an output signal which by means of OR gate 104 activates solenoid moving barrier 111 from its normal position obstructing the entrance to the acceptable coinpassageway for a sufficient period for the coin being examined to fall into the acceptable coin passageway 120. The outputs of AND gates 101, 102 and 103 are also connected by leads 131, 132, 133 to the accumulator 140, so that the output signal from each of those AND gates is transmitted to the accumulator to indicatethe denomination of the coin which has been accepted.

In order to discuss the operation of coin selector 10', we take for example the examination of a genuine 5- cent piece. The coinis dropped into coin entrance 20 and falls onto cointrack 30. The curved initial section 32 of coin track '30 converts the energy of the coins vertical motion into horizontalmotion along coin track 30. The coin first approaches and passes inductor 72,

causing the oscillator 80 to shift in frequency from 9.3 kHz. to approximately 10.67 kHz. As a result of this frequency shift, detector 81 produces a single output pulse which sets flip-flop 91 thereby providing a positive output indication from flip-flop 91. Detector 82 does not produce an output signal when the 5-cent piece passes inductor 72, as the frequency of oscillator 80 is not shifted to the range of detector 82, which is approximately from ll.87 to l2.l8 kHz. Flip-flop 92 is and past inductor 74, which is associated with the high frequency examination of IO-cent pieces. The presence of the S-cent piece in the vicinity of inductor 74 causes the associated oscillator 84 frequency to approach 455 kHz., increases above 455 kHz. and then falls past and below 455 kHz. as the S-cent piece approaches, moves past and away from the inductor 74. As a result the output of detector 85 produces a first pulse as the coin approaches inductor 74, setting flip-flop 94 and a second pulse as the coin proceeds away from inductor 74, which resets flip-flop 94; leaving flip-flop 94 without a positive output indication of the presence of an object which might be a lO-cent piece. The S-cent piece then approaches inductor 76 which is associated with -cent pieces. As the 5-cent piece passes by inductor 76, the oscillator 86 frequency is caused to approach, reach and then fall below 455 kHz.; causing a single output pulse from the detector 87, which sets flip-flop 96 producing a positive indication at the output of that flip- -flop. Finally the coin approaches and passes inductor 78. As in the case with inductor 74, the frequency of oscillator 88 which is associated with inductor 78 increases to, exceeds and then falls below 455 kHz. as the S-cent piece passes the inductor. This causes two output pulses to be produced by detector 89, setting and then resetting flip-flop 98; so that at the conclusion of the examination the output of flip-flop 98 is not a positive indication.

After the coin being examined has passed the entire set of inductors 70 a pulse is applied to the input of each of the AND gates 101, 102 and 103 on lead 105 from the strobe pulse generator 106, to interrogate the AND gates regarding the examination just completed. Since in this case the only positive indications from the flip-flops are on the inputs of.AND gate 103, only that gate produces an output signal which passes through OR gate 104 to activate solenoid 110 and also passes directly by lead 133 to accumulator 140 where the acceptance of a 5-cent piece is recorded. A suitable circuit for this purpose is shown and described below with respect to gates 934, 935 and 936 in FIG. 9.

An alternative low frequency circuit 500 is shown in FIG. 7. An oscillator 510 produces a low frequency signal, e.g.,: 5,000 kI-Iz., which is coupled to the transformer 512. The output of the transformer 512 is approximately 3 to 4 volts rms. That output is applied to terminals 521 and 522 ofa multiple leg bridge 520. The two legs of the bridge on the left side of FIG. 7, comprising the common or inductor branch, are the inductor 525 between terminals 522 and 523, and a resistor 526 between terminals 523 and 521. The inductor 525 may be similar to the typical inductor 200 which has already been described.

On the right side of the bridge shown in FIG. 7 there are three branch circuits in parallel between terminals 521 and 522, coupled at terminals 530,540 and 550 respectively to differential amplifiers 537, 547 and 557. In one leg of each ofthese circuits is a resistor 531, 541 or 551, connected from terminal 522 to terminals 530, 540 or 550 respectively. The other leg of each of the branch circuits contains a resistor-capacitor combination having the capacitative reactance sufficient to balance the inductive reactance of inductor 525 when a genuine coin of a particular denomination is adjacent the inductor 525. Each such leg has a fixed capacitor 532, 542 or 552 in parallel with a small trimmer capacitor 533, 543 or 553. In parallel with the capacitors in each circuit is a resistance sufficient to balance the inductors resistance, which for convenient range limitation comprises the series combination of variable resistor 534, 544 or 554 and fixed resistor 535, 545 or 555.

The inputs of each of the differential amplifiers 537, 547 and 557 is in effect across a bridge which can be adjusted to be in balance when a single denomination coin is adjacent inductor 525. Thus, for example, the capacitative reactance could be adjusted so that amplifier 537 would detect a balanced condition when a 5- cent piece is adjacent the inductor 525, and by similar adjustments amplifier 547 would for a l0-cent piece and amplifier 557 would for a 25-cent piece. The output of each of the differential amplifiers 537, 547 and 557 is fed to the input of a corresponding diode rectitier 538, 548 or 558, the outputs of each of which are fed to the corresponding limiting amplifiers 539, 549 and 559. The limiting amplifiers are cut off at zero signal input but saturate at very low input signal levels, and thereby convert the analog signal from their corresponding differential amplifier 537, 547 or 557 into a digital signal'which is at one level when the differential amplifier inputs are very close to balanced or are balanced, and at another level at all other times- (amplifier saturated). The digital outputs of limiting amplifiers 539, 549 and 559 are fedto logic circuitry 560 which may be of a type similar to that described with respect to FIG. 4. The low frequency circuit 500 is used in combination with a high frequency circuit, such as that shown in FIG. 4.

Typical values for a circuit according to FIG. 7 would be:

Resistor 526 2,000 ohms Resistors 531, 541, 55l 2.000 ohms- Variable Resistors 534, 544, 554 25.000 ohms max. Resistors 535, 545, 555 5,000 ohms Capacitors 532, 542, 552 01 1. F Variable Capacitors 533, 543, 553 300 pf max.

Inductor 525 may be 1,100 turns of No. 39 wire on a 22 mm pot core. Differential amplifiers 537, 547 and 557 may be Fairchild type 741 or the equivalent.

SECONDEMBODIMENT A coin selector 600 formed in accordance with the present invention in which all inductors are employed to examine for all denominations of coins in the accept able set, is shown in FIGS. 9 through 11. The mechanical arrangement of principal components is indicated by numeral 610. A coin may be introduced into the coin selector 600 through the coin entry 620. The coin then falls under the influence of gravity onto the deflector 630, which is sloped downwards in a direction away from the coin entry 620. The first coin track 631 onto which the coin entering the coin selector 600 through the coin entry 620 under the influence of gravity first falls is arranged so that the coin's vertical motion will be transformed into motion along the first coin track 631 with a minimum of coin bouncing.

Adjacent and contiguous to the deflector 630 and the first coin track 631 and the second coin track 632 is a sidewall'640 which is canted at a sufficient angle from the vertical to cause the face of a coin to bear against the wall 640, when the edge of a coin is resting on one of the coin tracks 631 or 632. An angle from the vertical greater than and less than 25 is acceptable for the sidewall 640; an angle of 9 having been found particularly satisfactory for a system having two tracks such as tracks 631 and 632. The coin tracks 631 and 632 are ordinarily arranged at a right angle to the sidewall 640.;A second sidewall 650 is arranged generally parallel to the sidewall 640 and is spaced away from sidewall 640 by a distance slightly greater than the thickness of the thickest coin which is to be selected by the coin selector 600. In FIG. 9, the lower portion of the sidewall 650 is not shown. The deflector 630 and the coin tracks 631 and 632 and the sidewalls 640 and 650 form acoin' passageway 660. The sidewall 640, the deflector 630 and the coin tracks 631 and 632 may conveniently be molded from the same piece of material. The accept 'gate (block 943 in the electrical portion of the diagram) is located approximately as indicated at 670. Further information concerning the mechanical details of an apparatus such as coin selector 600 is contained in British Provisional Specification Nos. 8386/72 and 8387/72, filed by the assignee of this application on Feb. 23, 1972.

In a coin selector 600, having a mechanical arrangement 610 of components, which is designed to examine and accept genuine coins of three different denominations, a set 710 of six inductors 711, 712, 713, 714, 715 and 716 is located along the coin passageway 660. Each of the inductors 711-716 is similar to the typical pot core inductor 200, shown in and described with respect to FIGS. 5 and 6. Alternatively, one or more of the inductors may be of a different type; for example, E-core inductors of the conventional type arranged with the three pole pieces in a line generally parallel to the coin track. A greater or lesser numberof inductors can also vbe utilized without departing from the present invention; for example, by utilizing a single inductor or pairof inductors for more than one function, as described below.

In one coin selector constructed in accordance with this invention for use with US. coins of the 5-cent, cent and -cent denominations, the first or arrival inductor 711 which is encountered by a coin moving through the coin selector 600 is a coil wound on an ,1 1 mm diameter pot core and is designed for operation in an oscillator circuit at frequencies in the vicinity of 455 kHz. It is located in a sidewall, e.g.; the sidewall 650 against which the coins are caused to bear by gravity and the angle off vertical of the sidewalls 640 and 650, at a position where it will be passed by all acceptable coins entering the coin selector when they fall onto the first coin track 631. The lower edge of the inductor 711 is located approximately /2 mm above the first coin track 631, to minimize the effects of coin bounce.

The second and third inductors are low frequency inductors, 712 and 713, which are two series connected coils each wound on 14 mm pot cores located opposite each other on either side of the passageway 660 in sidewalls 640 and 650 respectively. The series connected inductors 712 and 713 are designed for use in a low frequency bridge circuit operating at a frequency under 25 kHz, and typically at a frequency in the vicinity of 5 to 7 kHz. These low.frequency (LF) inductors 712 and 713 are located at the lower end of the first coin track 631 to permit the coin being tested to become stabilizedon the track before entering their field. The lower edge of the pot core of each of the inductors 712 and 713 is locatedslightly below the first coin track 631. The use of a pair of inductors 712 and 713 at opposite sides of the passageway 660 at the same position, makes the conductance examination at that position particularly sensitive to the thickness of coins being examined and therefore provides greater protection against attempts to defraud the coin selector with slugs or the like comprising a conductive body with a nonconductive coating which serves to adjust the spacing of the conductive body from the sidewall against which the slug bears; while reducing erroneous rejection of acceptable coins which move from side to side of the passageway 660 as they pass through the coin selector 600.

Located along the second coin track 632, reading from right to left in the direction of movement of a coin under the influence of gravity are inductors 714, 715 and 716, each ofwhich is a coil wound on an 18 mm diameter pot core which is located in the sidewall opposite that in which the arrival inductor 711 is mounted, sidewall 640, and each of which is designed for operation in an oscillator circuit in the vicinity of 455 kHz. Each such inductor 714-716 is located with the upper edge of its pot core at a distance orthagonal to second coin track 632, which distance is /2 to 1 mm greater than the diameter of the coin denomination with which it is associated, i.e.: inductor 714 being the 5-cent high frequency (HF) inductor, inductor 715 being the 25-cent HF inductor and inductor 716 being the l0-cent HF inductor.

Each of the HF inductors 711, 714, 715 and 716 is connected in an oscillator circuit 721, 724, 725 and 726 respectively. Each of these oscillator circuits is substantially the same as circuit 721 shown in detail in FIG. 10.

In oscillator circuit 721, the inductance of inductor 711 and capacitors 731, 732, 733 and variable capacitor 734 form a resonant circuit. Capacitor-733 may be a temperature compensating capacitor. Variable capacitor 734 is used for tuning the resonant circuit. Capacitors 731 and 732 form a high frequency voltage divider, the voltage across capacitor 732 being applied between ground andthe emitter of common base oscillator transistor 735, which may be a type 2N3856A type transistor, through a 200 ohmmax. adjustable resistor 736, which adjusts the positive feedback to stabilize the oscillator. The signal applied to the emitter appears amplified and in phase between ground and the collector of transistor 735, resulting in a self-sustaining oscillation. The DC emitter bias of the transistor 735 is established by resistor 737, which is in series with an HF blocking inductance 738. Positive DC voltage is applied to the collector of transistor 735 through HF blocking inductor 739, which is in series with a ohm resistor 740 which lowers the Q of inductor 739 sufficiently that it doesnt significantly affect the resonant circuit. Resistors 741 and 742 establishthe base bias of the transistor 735, and by-pass capacitors 743 and744 prevent high frequency fluctuations of the 15V- supply and of the base potential.

At the output of each of the oscillators 721, 724, 725 and 726 is a high Q HF detector circuit, 751, 754, 755 and 756 respectively. Each of these detector circuits is substantially the same as detector circuit 751 shown in FIG. and is connected to its respective oscillator as indicated in that figure. 1

The input signal for detector circuit 751 is the voltage across capacitor 732 of the oscillator 721. The signal is applied to a two-stage 455 kHz filter 761, such as Murata type SF-455-D ceramic filter distributed by The Murata Corp. of America, New York, New York. Two 300 ohm resistors 762 and 763 are provided to properly match the impedance of the filter 761. Capacitor 764 couples the two stages of the filter 761; its value selected to provide the desired bandpass of the detector 751. Diodes 765 and 766 form a peak rectifier, the voltage at the output of diode 766 being representative of the peak-to-peak voltage at the output of the filter 761. Filtering is provided by capacitor 767 and resistor 768. The filtered signal from resistor 768 is applied to the base of the common emitter DC switching transistor 769 such as a'type 2N2925 transistor. When a sufficient amplitude signal is applied to the base of transistor 769, its impedance switches from high to low, causing the collector voltage, supplied from a 5,600 ohm resistor 770, to drop from the supply voltage (5 volts DC) to nearly ground potential. A l microfarad capacitor 771 connected from the collector of transistor 769 to ground provides extra filtering to assure a clean waveform substantially free of oscillator frequency variations and noise.

In the case of some of the oscillators, such as oscillators 721 and 726, it may be desirable to have a detector, such as detectors 757, 758 and 759, which are tuned to a frequency other than that of the other detectors 751, 754, 755 and 756, and have a lower Q than those other detectors. A typical detector of this type, detector 758, is also shown in FIG. 10. Transformer 781 is a conventional, adjustable-core IF transformer of the type commonly used in radio receivers and capacitor 782 is a capacitor of the type conventionally used and packaged with such IF transformers. Resistor 783 is an impedance matching resistor selected to match transformer 781. Diode 784 provides a rectified output representative of the amplitude of the signal at the transformer output tap to which the cathode of the diode 784 is attached. Capacitor 785, resistor 786, switching transistor 787 capacitor 788 and resistor 789 each performs the same functions as the corresponding components. of detector 751.

The low frequency (LF) oscillator 722 produces a low harmonic content sine wave of approximately 5 kHz. As shown in FIG. 11, its resonant circuit is formed by the inductance of the primary coil 811 of the transformer 810 and capacitors 813 and 814. The voltage across capacitor 813 is applied to the base of a common collector connected transistor 815, which produces a current gain at its emitter which is used to drive the emitter of a common base connected transistor 816. Both the transistor 816 and the transformer 810, to which the collector of the transistor 816 is connected at a tap near the DC end of the primary coil 811, provide gain so that the overall loop gain is unity. A suitable type of transistor for use as transistors 815 and 816 is type 2N3856A. The value of resistor 817 is selected to provide the desired amount of feedbakc. Resistor 818 provides appropriate emitter bias for transistor 815. Resistors 819 and 820 provide the emitter bias for transistor 816. They also affect stability and the amount of feedback. Resistors 821 and 822, which have equivalent values, provide the bias for the base of transistor 816. Resistor 823 provides signal isolation between the bases of the transistors 815 and 816 while leaving their operating points substantially the same. Capacitor 824 is the base by-pass capacitor for transistor 816.

The output of the LF oscillator 722 from the secondary coil 812 of transformer 810 is applied to bridge circuit 752. The value of the resistor 834 in one of the leads from the oscillator 722 to the bridge 752 is selected to provide the desired amount of oscillator voltage to the bridge 752, thereby affecting the sensitivity of all of the LF detection circuits. Two legs of the bridge circuit 752, those comprising resistor 831, and inductors 712 and 713 and resistors 832 and 833, are used in common with all three of the low frequency detector circuits 774, 775 and 776. The other two legs of the bridge comprise a portion of each individual detector circuit, only detector 774 being shown in detail in FIG. 11.

The LF inductors 712 and 713 are connected in series in one leg of the bridge 752 so that when a coin passing between the LF inductors affects the magnetic field between them, both the amplitude and phase of the LF voltage applied across the inductors 712 and 713 changes. The value of resistor 831 has been selected to have substantially the same impedance in the absence of coins and other field influencing objects between the inductors 712 and 713, as that .of the leg comprising the inductors and resistors 832' and temperature compensating resistor 833, which compensate for changes in impedance due to the heating of the wires of the inductors 712 and 713.

Each of the LF detectors 774, 775 and 776, the 5- cent, 25-cent and lO-cent LF detectors respectively, is similar to detector 774 shown in FIG. 11 and is similarly connected at its input as a part of bridge 752. One leg of the bridge 752 in detector 774 comprises a fixed resistor 835 in series with a variable resistor 836, the resistors beingin parallel with a series connected to variable capacitor 837 and temperature compensating capacitor 838 (to compensate for changes in the reactive component in the bridge by heating of the wires of the inductors 712 and 713). The variable resistor 836 and variable capacitor 837 are adjusted so that when a genuine coin of the associated denomination (a 5 cent piece in the case of detector 774) passes between the LF inductors 712 and 713, the bridge will be brought substantially into balance. I

The active elements of the detector 774 comprise an operational amplifier 840, e.g.: a Faircliild type 741 amplifier, a peak detector comprising two diodes 853 and 854, and a switching transistor 860. In order to make the amplifier 840 linear for small input signals, in the vicinity of a null of the bridge 752, the noninverting input (terminal 3) is biased to midway between the DC power supply voltage and ground potential by equal value resistors 841 and 842. Resistor 842 is bypassed by capacitor 843 to maintain one side of the bridge 752 at LF ground potential. The inverting input (terminal 2) of the amplifier 840 is isolated from the DC bias potential by blocking capacitor 846. Resistors 844 and 845 are large (e.g.: 100,000 ohms) and the input impedance of the amplifier 840 is high, so resistors 844 and 845 have substantially no effect on the operating point of the amplifier 840. The output of the amplifier (terminal 6) reproduces the inverse ofthe signal applied to the inverting input (terminal 2). Feedback from the output terminal to the inverting input is provided by the network of two 100,000 ohm resistors 847 and 848, and capacitor 849 to stabilize the quiescent point of amplifier 840 at the value of the noninverting input voltage. The divider primarily comprising resistors 847 and 848 is in parallel with resistor 851 connected to the output of the amplifier 840 and provides negative feedback to stabilize the LF gain at approximately 200'.

A DC blocking capacitor 852 couples the LF output of amplifier 840 to a peak detector comprising diodes 853 and 854. Two resistors 855 and 856 and two capacitors 857 and 858 comprise a filter to smooth the rectified output of the diodes 853 and 854. The output of that filter is applied to the base ofa common-emitter coupled switching transistor 860, which may be a type 2N3392 transistor. The DC base bias of the transistor 860 is established by the divider comprising resistors 859, 856 and 855 and diodes 854 and 853. A small capacitor 861 (e.g.: 0.0018 microfarad) between collector and base of the transistor 860 and a capacitor 862 (e.g.: 0.1 microfarad) from collector to ground provides further filtering to assure a smooth switching waveform from transistor 860. A power supply filter capacitor 863 is connected between the source of detector power and ground.

When the bridge 752 is unbalanced, its normal quiescent condition in the absence of an acceptable coin of the proper denomination from between the LF inductors 712.an d 713, the rectified signal voltage from the diodes 853 and 854 holds the transistor 860 off, so that the collector of transistor 860 is at substantially the collector supply potential (here, 5 volts DC). When a coin or other object causes the inductance of the inductors 712 and 713 to change so that the bridge 752 is substantially balanced, the input to the base of transistor 860 will drop below the switching threshold, transistor 860 will switch on, substantially all of the collector supply voltage will be applied across the collector supply resistor 864 and the output of the detector 774 at the collector of transistor 860 will be substantially ground potential.

In order to discuss the operation of coin selector 600, we take for example the examination of a genuine cent piece. After the coin is dropped into coin entrance 620 and falls intothe first coin track 631, it first approaches and passes arrival inductor 711, causing the oscillator 721 to shift upwards in frequency from its idling'frequency of approximately 386 kHz.

The oscillator 721 has been designed and its idling frequency has been selected so that any non-magnetic electrically conductive coinlike object passing the arrival inductor 711 will cause the frequency of oscillator 721 to rise at least to 10 kHz above idling frequency. One of the arrival detectors 758 is tuned to this higher frequency, and therefore produces an output whenever any object passing the arrival inductor 721 causes a shift to that frequency. If the object passing inductor 711 has characteristics similar to a single coin of a denomination with which the coin selector 600 is intended to operate, the frequency from oscillator 721 will pass twice through the bandpass of the first arrival detector 758, first as the frequency increases and then as it decreases, causing the detector 758 to produce two output pulses. The pulses from the detector 758 are amplified and shaped by amplifier 901 and applied to a NAND gate 902 and the triggering input of a J-K flip-flop 903. In the usual case when a coin test is started flip-flops 903 and 904 which are arranged as a four-bit counter have been reset, and they and the amplifier 901 are producing an output signal of the same polarity. When the arrival detector 758 produces its first pulse, the output of amplifier 901 is switched momentarily to the opposite polarity, causing a pulse to appear at the output of the NAND gate 902 and triggering flip-flops 903 and 904. Both before and after th is first pulse, both inputs to NAND gate 905 from the Q outputs of the flip-flops 903 and 904 are the same, so no signal appears at the output of the NAND gate 905. The pulse from the NAND gate 902 is coupled by capacitor 906 to switching transistor 907,turning it on and producing a pulse at its output which drives the reset amplifier 909 at its input point 910. Resistor 908 is the base bias resistor for transistor 907.

When a second pulse is produced by detector 758, the signals applied to each of NAND gate 902 and NAND gate 905 are all of the same polarity and therefore each produces .no output. In the event that two closely spaced coins pass the arrival inductor 711; detector 758 produces a third and a fourth pulse. The third pulse does not affect the output of NAND gate 902, but NAND gate 905 is caused to generate an output by the third pulse, which triggers monostable 911 causing it to produce an 800 millisecond pulse which in turn activates the reset amplifier 909 for that period and thereby prevents the coin selector 600 from examining and accepting either of the coins present on the flight deck at that time. This third pulse is counted by the contiguity counter (flip-flops 903 and 904) which enable NAND gate 905. Flip-flops 903 and 904 are reset each time a coin departs from the coin selector by a signal from the departure detector 757.

The oscillator 721, inductor 711 and the second arrival detector 751 have been adjusted so that any genuine coin ofa denomination, which the coin selector 600 is intended to accept, passing the inductor 711 will cause the frequency of the oscillator 721 to rise above 455 kc, producing a pulse which sets flip-flop 912 producing a continuous output which drives an amplifier 913 and enables the collector terminal 916 of transistor 915 for purposes which will be described below in connection with-the departure detector 757.

quency bandpass above the maximum frequency which the oscillator produces for geniune coins, e.g.: approximately 472 kHz. In the event that the frequency of the oscillator 721 reaches the frequency to which the copper detector 759 is tuned, the copper detector 759 produces a pulse which is amplified by an amplifier 917 and applied to the input of monostable 911 which activates the reset signal in the manner previously described.

After passing the arrival inductor 711, the lO-cent coin moves under the force of gravity to the low frequency inductors 712 and 713. As it passes those inductors, the appropriate detector .776 produces an output pulse triggering and setting flip-flop 976, flip-flops 974 and 975 being left in the reset condition since the lO-cent coin will not cause the frequencies produced by oscillators 724 and 725 to rise to the tuned fre quency of detectors 774 and 775. As in the preceeding embodiment, in the event that a coin passing one of the HF inductors has characteristics which cause its associated oscillator to rise above the tuned frequency of its detector; that detector will produce two output pulses as the coin passes the inductor which will first set and then reset the associated flip-flop.

The lO-cent coin then drops from the first coin track 631 to the second coin tract 632 and moves successively past HF inductors 714 and 715. A lO-cent piece will not cause the frequencies of the respective oscillators 724 and 725 to be shifted sufficiently from their idling frequencies of approximately 396 kHz and 403 kHz to reach the 455 kHz tuned frequency of HF detectors 754 and 755. In the case of inductor 716 and oscillator 726, however, a genuine l-cent piece will cause the frequency of the oscillator 721 to change from its idling frequency of approximately 411 to, but not above, the bandpass centered on 455 kHz of the 10-cent HF detector 756. The detector 756 therefore produces a single pulse which triggers and sets lO-cent HF flip-flop 956.

In addition to participating in the HF examination for lO-cent coins, lO-cent oscillator 756 drives the departure detector circuit 757, which is similar to the first ar rival circuit 758 and is similarly tuned approximately to kHz above the idling frequency of the oscillator with which it is associated. When the frequency of oscillator 726 first passes through the pass band of the departure detector 757, flip-flop 918, which acts as a two bit counter, is triggered into the set condition. This, however, does not affect switching transistor 915, the base of which is coupled to the Q output of flip-flop 918 by capacitor 919, because of the polarity of the pulse from capacitor 919 and the bias of the base by resistor 920'. When the frequency of the oscillator 726 approaches the idling frequency again, however, a second pulse from departure detector 757 again triggers flip-flop 918, which this time causes a pulse of the appropriate polarity to be applied from capacitor 919 to the base of switching transistor 915. The transistor 915 is then switched off permitting the collector terminal 916 of transistor 915 to go to the potential produced by amplifier 913. If amplifier 913 is producing a signal as a result of the second arrival detector 751 having set flip-flop 912 and nothing having caused flip-flop 912 to be reset, a pulse enabling signal or strobe is applied to AND gates 934, 935 and 936. In the event that the other two inputs of any of these gates are then each receiving a signal, as is true for AND gate 936 in the case ofa genuine lO-cent coin, that gate produces an output signal which is indicative of the acceptability and denomination of the coin examined. The signal from each of the AND gates 934, 935 and 936 is transmitted to OR gate 937 and to the accumulator 950. The base of common collector switching transistor 940 is coupled by a capacitor 938 to the output of OR gate 937. When a signal is applied to any of the inputs of OR gate 937, switching transistor 940 is momentarily switched on activating the solenoid 942 which controls the coin acceptance gate 943.

The accumulator 950 has a straightforward design of the type known to those skilled in the art. It transmits a signal by means represented by line 751 to the controlled equipment or vending machine 960 indicating that the coin selector 600 has accepted sufficient funds to satisfy the amount required as indicated by a signal by means represented by line 951 from the controlled equipment 960. In addition, the accumulator 950 receives a signal by means represented by line 962 from the controlled equipment 960 indicating that the desired response, e.-g.,: vending, is occurring; which signal is used to reset the accumulator 950. The accumulator also provides a signal by means represented by line 952 to control a change giver 970.

The coin selector 600 has two other reset functions not previously described. The first is a power source monitoring reset 980 which transmits a signal to the accumulator 950 and a signal to the input 910 of reset amplifier 909 for a fixed period after each time when the power to the coin selector 600 is turned on. This circuit tends to prevent interference withthe proper operation of the accumulator 950 by clamping the accumulator reset line until the power provided for its operation has stabilized. The second is controlled by the strobe pulse at the collector terminal 916 of transistor 915. A common emitter switching transistor 990 is triggered on by a signal at its base at a time after the strobe pulse which is defined by RC circuit comprising resistors 991 and 992 and capacitor 993. The collector of this transistor 990 is also connected to the input 910 The power of both the method and apparatus utilizing LF and HF examinations of coins for discriminating between acceptable and unacceptable coins has been demonstrated in a test of a prototype apparatus of the type described which was designed and adjusted to accept greater than percent of genuine U. S. 5-cent, lO-cent and 25-cent coins. None of 138 foreigncoins and slugs which were examined by the prototype apparatus were accepted, although many of the coins and slugs were selected for their ability to pass conventional coin selectors. Of these unacceptable coins and slugs, 16.7 percent were rejected only as'a result of the LF examination and 24.6 percent were rejected only as a result of the HF examination, 29 percent were acceptable as different denominations on the HF and LF examinations but were rejected as a result of the requirement that the coin examination indicate acceptance with respect to the same denominations at both the low frequency and the high frequency. The remaining 55.8 percent were rejected as a result of both the HF and LF examinations.

THIRD EMBODIMENT A coin selector 1000 formed in accordance with the present invention having a mechanical arrangement 1010 of certain components is shown in FIG. 12. A coin may be introduced into the coin selector 1000 through the coin entry 1020. The coin then falls under the influence of gravity onto the deflector 1030, which is sloped downwards in a direction away from the coin entry 1020. The deflector 1030 onto which the coin initially falls so that the vertical motion of a coin entering the coin selector 1000 through the coin entry 1020 under the influence of gravity will be transformed into motion along the first coin-track 1031 with a minimum of coin bouncing.

Adjacent and contiguous to the deflector 1030 and the coin track 1031 is a sidewall 1050 which is canted at a sufficient angle from the vertical to cause the face of a coin to bear against the wall 1050, when the edge to the sidewall 1040. In FIG. 12, the lower portion of the sidewall 1050 is not shown. The deflector 1030 and the coin track 1031 and the sidewalls 1040 and 1050 form a coin passageway 1060. The sidewall 1040, the deflector 1030 and the coin track 1031 may conveniently be molded from the same piece of material. The accept gate (block 1243 in the electrical portion of the diagram) is located approximately as indicated at 1070.

In a coin selector 1000, which is designed to examine and accept genuine coins of three different denominations, a set 1110 of four inductors 1111, 1112, 1113, and 1114 are located along the coin passageway 1060. Each of the inductors 1111-1113 is similar to the typical pot core inductor 200, shown in and described with respect to FIGS. and 6 above. Inductor 1114 in the embodiment shown in a 18 mm X 13 mm E-core inductor, arranged with the three pole pieces in a line generally parallel to the coin track.

In one coin selector constructed in accordance with this invention for use with U.S. coins of the S-cent, cent, and 25-cent denominations, the first or arrival inductor 1111 which is encountered by a coin moving through the coin selector 1000 is a coil wound on an 18 mm diameter pot core and is designed for operation in an oscillator circuit at frequencies in the vicinity of 400 to 500 kHz. It is located in a sidewall, e.g.: the sidewall 1050 against which the coins are caused to bear by gravity and the angle off verticalof thesidewalls 1040 and 1050,'at a position where it will be passed by all acceptable coins entering the coin selector when they fall onto the first coin track 1031. The lower edge of the inductor 1111 is located approximately 1 mm. above the first coin track 1031.

The second and third inductors are low frequency inductors, 1112 and 1113, which are two series connected coils each wound on 14 mm. pot cores located opposite each other on either side of the passageway 1060 in sidewalls 1040 and 1050 respectively. The series connected inductors 1112 and 1113 are used in a low frequency bridge circuit 1152 which is driven by oscillator 1122, similar to the bridge circuits shown in FIGS. 7 and 11. The low frequency (LF) inductors 1112 and 1113 are located at the lower end of the first coin track 1031 to permit the coin being tested to become stabilized on the track before entering their field. The lower edge of the pot core of each of the inductors 1112 and 1113 is located approximately 4 mm. below the coin track 1031. I

The fourth inductor 1114 is located in the opposite sidewall 1040 of the passageway 1060 from the first inductor 1111. Like the first inductor 1111, the fourth inductor 1114 is for use in a high frequency (HF) circuit. In the embodiment shown, the fourth inductor 1114 is located above inductors 1112 and 1113, with its bottom edge approximately 14 mm. above the track, and aligned with the centers of its three pole pieces parallel to the coin track 1031 at that point. The center poles of all three inductors 1112, 1113 and 1114 are located on a line orthogonal to the track.

The above-described arrangement of inductor locations has been selected for a particular set of coin denominations. The location, size and operating frequency of the first HF inductor 1111 cause the examination results to be a function of both diameter and surface material characteristics of the coin. Similarly, the results of examination by the second HF inductor 1114, which is on the opposite side of the coin passageway from the sidewall 1050 on which the face of the coin bears, are a function of diameter and surface material characteristics, and also of distance of the conductive material of the coin from the inductor 1114. Because the two HF examinations are made independently from opposite sides of the coin, the coin selector 1000 is particularly secure against slugs which might be made by laminating non-conductive material to conductive material in an effort to simulate the conductivity of a different conductive material which is used in genuine coins.

Each of the HF inductors 1111 and 1114 is connected in an oscillator circuit 1121 and 1124 respec tively; or alternatively a single oscillator circuit may be provided, along with appropriate switching circuitry, for use with both of the HF inductors; as the two HF inductors are utilized sequentially. Each of these oscillator circuits is substantially the same as circuit 721 shown in FIG. 10. As the output of each of the oscilla' tor circuits 1121 and 1124 is a plurality of high Q HF detector circuits 1154-1156 and 1158 and 1194-1196 and 1157 respectively. Each of these detector circuits is substantially the same as detector circuit 751 or detector circuit 758 shown in FIG. 10, however, the bandpass frequency of the element of the detector circuits corresponding to filter 761 of detector 751 is not necessarily 455 kHz.

The idling frequency of oscillator 1121 is approximately 420 kHz. The first HF or arrival detector 1158 is a circuit such as the arrival detector 758 of FIGS. 9

and 10. tuned to a frequency slightly above the idling frequency (e.g.,: '430 kHz), and operates in the same fashion as detector 758.

Detectors 1154, 1155 and 1156, circuits similar to detector 751 of FIGS. 9 and 10, are tuned to the appropriate peak oscillator frequency caused by a genuine 5-cent, 25-cent and lO-cent coin, respectively, passing inductor 1111. In one coin selector these frequencies were approximately 470, 495 and 420 kHz respec tively. Similarly, detectors 1194, 1195 and 1196, circuits monitoring the output of oscillator 1124 which are also similar to detector 751, are tuned to the approximate peak oscillator frequency caused by a genuine S-cent, 25-cent and lO-cent coins, respectively, passing inductor 1114. In one coin selector these fre quencies were approximately 460, 460 and 420 kHz respectively when the idling frequency of the oscillator 1124 was 400 kHz. When as, in this case, the detector frequency is the same for two acceptable denominations, one of the detectors can be eliminated by appropriate changes in logic circuitry. The oscillator frequency characteristics and the precise frequency and bandwidth of each of the detectors is a matter of selection for the desired tolerances by adjustment of the location and design of the inductors 1111 and 1114 and the design of the oscillator circuit.

The remaining detector is the departure detector 1157, a circuit similar to circuit 758 of FIG. 10. It is tuned, like detector 1158 to a frequency slightly above the idling frequency of the oscillator 1124, the output of which it monitors; however, like detector 757, detector 1157 is connected to logic circuitry arranged to identify the second time when the frequency of oscillator 1124 goes through its bandpass as an indicia of the departure of a coin from the inductor regions of the track 1031.

Appropriate logic circuitry for use in connection with the output of the detectors of this embodiment may be constructed in accordance with the principles discussed in previous embodiments. The logic circuit should in each case provide an output signal indicative of the presence of an acceptable coin ofa given denomination only in the event that, during the period between an arrival and a departure signal, (I) the peak frequencies of oscillators 1121 and 1124 are within the respective bandpass for that denomination, (2) the appropriate branch of bridge 1152 for that denomination is nulled, and (3) that the null of bridge 1152 and the peak detected by the detector 1194, 1195 or 1196 occur within a predetermined tolerance of simultaneity. Alternatively, HF inductor 1114 may be offset along the line of coin movement from the LF inductors 1112 and 1113,-in which case the logical relationship between the output of the detectors associated with each for optimum performance should include an appropriate time delay, e.g.,: by use of a monostable multivibrator.

The basic operating block diagram of suitable logic for this embodiment is suggested by the remainder of FIG. 12. If a genuine coin of an acceptable denomination is inserted into the coin selector 1000, upon approaching inductor 111 1, the increase in frequency of oscillator 1121 is detected by the arrival detector 1158 -and'flip-flop 1258 is set, thereby producing an output signal at its terminal Q. As the coin passes the inductor 1111, the frequency continues to rise to a peak frequency within the range of one of the detectors 1154-1156, depending upon its denomination. The detectors operate in the same fashion as the detectors 754-756 shown in FIG. 10, producing one output pulse for each time the oscillator frequency passes through its bandpass; this producing a single pulse only when the peak oscillator frequency is within the detectors bandpass. The outputs of the detectors 1154-1156 are each applied to one input of AND gates 1264-1266, respectively; the other input of each of the AND gates being connected to the Q output of flip-flop 1258, the arrival. signal from which enables the pulses to pass to flip-flops 1254-1256, respectively. Depending upon the denomination of the coin tested, at least one of the flipflops 1254-1256, is set and remains set after the coin has passed the inductor 1111. The remaining flip-flops either are not set at all or are set and then reset in the manner previously described with respect to FIG. 10.

When the frequency of oscillator 1121 decreases nearly to idling frequency, it again passes through the bandpass of arrival detector 1158, providing an output pulse which triggers flip-flop 1258 into reset condition. The Q output of flip-flop 1258 produces an output which sets flip-flop 1259 and thereby enables AND gates 1294-1296, as described below.

As the coin approaches inductors 11 12-1114, the frequency of oscillator 1124 associated with inductor 1114 increases. The increase is first detected by departure detector 1157 which produces an outut pulse as the frequency passes through its bandpass; which output pulse sets flip-flop 1277, causing the Q output of the flip-flop to supply an enabling signal to AND gates 1294-1296. In the event that one of the detectors 1194-1196 (in this example, the detector for the same denomination previously indicated) detects a peak oscillator frequency within its bandpass, in the manner previously described, it produces a single output pulse. If this occurs during the period when the one of the LF detectors 1174-1176 for the same denomination coin detects a null in the output of bridge 1152, then there is a coincidence of signals on all of the inputs to the one of the AND gates 1294-1296 corresponding to that denomination coin, and a pulse is passed to and sets' the corresponding flip-flop 1274, 1275 or 1276. In the event that the frequency of the oscillator 1124 passes twice through the bandpass of one of the detectors 1194-1196 while the corresponding one of the LF detectors detects a null, as a result of a peak oscillator frequency above its bandpass, the corresponding flip-flop 1274, 1275 or 1276 is first set and then reset. In the event that one of the LF detectors 1174-1176 produces two nulls, one as the coin approaches and one as the coin departs from inductors 1112-1113, the pulse produced by the LF detectors will not coincide with a single pulse from the corresponding HF detector 1194-1196, and there will be no coincidence of signals at the corresponding AND gate 1294, 1295 or 1296 and the corresponding flip-flop 1274, 1275 or 1276 will not be set.

When the coin departs from inductor 1114 and the frequency of oscillator 1124 again approaches idling frequency, the frequency passes through the bandpass of departure detector 1157 producing a pulse which guses flip-flop 1277 to be reset. The transient at the Q output of the flip-flop 1277 passes through capacitor 1278, momentarily increasing above ground potential the voltage of the common point between capacitor 1278 and ,resistor1279 and thereby applying a pulse to one input of each of the AND gates 1234-1236. If, when the AND gates receive that pulse, one of them is receiving a signal from the Q output of its corresponding flip-flop 1274, 1275 or 1276, the signal is passed to the accumulator 1260 as an indication of denomination and via OR gate 1237 and AND gate 1239 to activate solenoid 1242 to remove the accept gate 1243 (designated by 1070 in the mechanical portion of the Figure) from the coin path. Alternatively, a coin presence indicative signal produced by a coin presence sensor 1072 along the coin path above the accept gate 1243 (1070) and an appropriate logic circuit 1238 may be used to activate the solenoid 1242. The accepted coin then falls past a coin presence sensor 1073, which operates in conjunction with the logic circuit 1238 to produce a signal when the coin has cleared the accept gate 1243 (1070) which is applied to inhibit AND-gate 1239, deactivating the solenoid 1242, and is also applied to reset all of the flip-flops by means omitted from FIG. 12. This signal from the logic circuit 1238 is also applied to the accumulator 1260 to cause it to accept the indication of denomination.

FOURTH EMBODIMENT FIG. 13 shows a coin selector 1300 having a mechanical arrangement 1310 of components similar to the mechanical arrangement 1010 of coin selector 1000 of FIG. 12, except that only a single inductive sensing station 1314 is utilized. The inductive sensing station 1314 may comprise a single inductor such as the pot core inductor 200 shown in FIGS. and 6, or a pair of inductors on opposite sides of the coin passageway as described with respect to FIG. 12. The inductive sensing station 1314 is connected in a multileg bridge circuit 1320, similar to the bridges shown in FIG. 7 or FIG. 11, in which the station 1314 and resistor 1326 comprise the common leg of the bridge 1320. Unlike the previously described bridge circuits, however, the oscillator input signal to the bridge 1320 is an AC coupled high frequency signal from HF oscillator 1311 and an AC coupled lower frequency signal from LF oscillator 1312 which is connected in parallel with HF oscillator 1311. Thus both a HP and a LF signal are concurrently applied to the sameinductive sensing station 1314. The LF leg of the bridge 1320, comprising resistor 1331, capacitor 1332, variable capacitor 1333, resistor 1335 and variable resistor 1336, is tuned by adjustment of the component values so that the bridge will be balanced with respect to the LF component of the input signal when'a genuine coin of a particular denomination is directly adjacent the inductive sensing station 1314. The output signal from this LF leg passes through a filter 1336, which blocks the HF component of the signal, to a differential amplifier or comparator 1337 producing an output signal which is rectified by diode rectifier 1338 and converted to a digital signal by limiting amplifier 1339 for use by subsequent logiccircuitry 1350 in a manner as is described with respect to FIG. 7 or FIGS. 9 and 11. Similarly, the HF leg of the bridge 1320, comprising resistor 1341, capacitor 1342, variable capacitor 1343, resistor 1344 and variable resistor 1345 is tuned for a balance of the HF component of the input signal when the same coin is in the described position. The output signal from this HF leg passes through a filter 1346, which blocks the LF component of the signal, to a'co'mparator'1347 producing an output signal which is rectified by diode rectifier 1348 and converted to'a digital signal by limiting amplifier 1349 for subsequent use by logic circuitry 1350 in a similar fashion to the digital signal desired from the LF leg of the bridge 1320. When the logic circuitry 1350 receives concurrent signals indicative of an acceptable coin from the LF and HF comparators 1337 and 1347 for the same denomination, it produces a signal indicative of the acceptability of the coin and of its denomination.

It will be readily apparent that a coin selector such as coin selector 1300 can be constructed for a plurality of denominations of coins by providing additional legs on the bridge 1320. As an alternative to AC coupling of the two oscillators 1311 and 1312 in parallel and using a single bridge for both high and low frequency tests; a separate HF and LF bridge can be used, each having a separate inductor winding or windings on common inductor core or cores.

FIFTH EMBODIMENT A coin selector 310 formed in accordance with the present invention and employing digital frequency identification techniques is shown in FIG. 8. The differences between this coin selector and the coin selectors previously described are in the electric circuit. Like the circuit of FIG. 4, this circuit employs four oscillators 380, 384, 386 and 388, one in connection with each of the four inductors 372, 374, 376 and 378. The mechanical structure and location of inductors 372, 374, 376 and 378 may be the same as those shown in FIGS. 1 and 2 or FIG. 3; however, the method and apparatus described below may be readily adapted to other embodiments. Each of the oscillators normally oscillates at its idle frequency in the absence of conductive objects in the vicinity of the associated inductor. The frequency changes when a conductive object is in the circuitry of its associated inductor. A clock 450 generates pulses at a rate selected for example, in the range of 300 to 400 pulses per second, each pulse being employed to trigger on the monostable multivibrator (or one shot) 451 for a precise period of 2 milliseconds.

The output of monostable 451 is applied to one input of each of the AND gates 400, 401, 402 and 403. The outputs of the oscillators 380, 384 386 and 388 are connected to another input of their respective AND gates 400, 401, 402', 403. Each of the four outputs of a conventional two-stage counter 452, is connected to the third input of one of the gates 400, 401, 402 and 403. The counter 452, the input of which is connected to the clock 450 output, cyclically produces one output pulse on each output for every four clock pulses; the

duration of each such output pulse' from the counter 452 being approximately the period between clock pulses, which is longer than the period of the output pulse of the monostable 451.

When a pulse'from the counter 452 is applied to one of the AND gates, for example gate 400, the gate will be activated during the precision period established by the pulse from the monostable 451, permitting the output pulses from the oscillator 380 to pass through the gate 400. Similarly gates 401, 402 and- 403 pass pulses from their respective oscillators 384, 386 and 388 when activated by both a pulse from the monostable 451 and the two-stage counter 452.

The outputs of the AND gates 401, 402 and 403 are applied to the inputs of OR gate 404, the output of which is applied'to the input of frequency divider 405 which divides the pulse rate of signals received from gate 404 by a factor of 16. Thepurpo'se of this divider is to simplify the use of a single multistage counter 407 for counting both the high frequency outputs of oscillators 384, 386 and 388 and the low frequency output of oscillator 380. The output signals from AND gate 400, which is associated with oscillator 380, and the output signals from divider 405 are connected to OR gate. 406 and thence are applied to the multistage counter 407.

The parallel output of the counter 407 is connected to anumber of decoders 420 through 429; one being shown here for each item to be decoded, although in some practical devices it will be possible to use a single decoder for more than one function when the number to be decoded is significant in more than one way. The functions of the decoders are for the lower and upper limit counts respectively of the various tests as follows: 5 bulk 420 and 421, 10 and 25 bulk 422 and 433, 5 high frequency 424 and 425, 10 high frequency 426 and 427, and 25 high frequency 428 and 429. The output of each of the lower limit decoders in 420, 422, 424, 426 and 428 is connected to the set input of its respective flip-flop 430, 432, 434, 436 or 438. When the count for a particular lower limit decoder is reached in the counter 407, the flip-flop associated with that decoder will be set. The outputs of each of the upper limit decoders 421, 423, 425, 427 and 429 are connected to one input of its respective OR gate 431, 433, 435, 437 or 439; the output of which is connected to the reset input of respective flip-flop 430, 432, 434, 436 or 438. When the count for a particular upper limit decoder is reached the associated flip-flop will be reset. At the conclusion of each counting period, determined by the length of the pulse from one shot 451, a short duration pulse on lead 498 is applied to one input of each of the AND gates 440, 442, 444, 446 and 448. The other inputs of each of these gates are connected to the outputs of flip-flops 430, 432, 434, 436 and 438 respectively. If any of these flip-flops have been set and not reset during the preceding sampling period, an output signal will be applied to an input of one of the gates 440, 442, 444, 446 or 448. The pulse which is then produced at the output of the gate will increase the count by l in the associated two-stage counter 441, 443, 445, 447 or 449. The pulse on lead 498 is also applied to the reset input of counter 407, resetting it to starting condition, and after a delay caused by delay cicuit 499 the pulse is applied via OR gates 431, 433, 435, 437 and 439 to reset flip-flops 430, 432, 434, 436 and 438.

The outputs of the two-stage counters 441, 443, 445, 447 and 449 are each connected to one or more of the AND gates 454, 456 and 458 which are associated with 5-cent, l-cent and 25-cent pieces respectively. The inputs ofAND gate 454 include the outputs of counters 441 and 445; the inputs of gate 456 include the outputs of counter 443 and 447; and the inputs of gate 458 include the outputs of counters 443 and 449. The third input of each of the AND gates 454, 456 and 458 is the previously described lead 498. When one of the twostage counters 441, 443, 445, 447 or 449 has received four pulses from its input AND gate, that counter produces an output pulse indicating that the associated oscillator has been operating at the frequency indicative of an acceptable coin for four inspections. When all three inputs of one of the AND gates 454, 456 or 458 concurrently receive a signal, .that gate produces an output pulse to the accumulator 410 indicating the presence of an acceptable coin of its associated denom ination.

What I claim is:

1. A method for examining conductive coins with respect to both theirauthenticity and their denomination within a set of acceptable coins of various denominations comprising the steps of generating a first electromagnetic field of a low frequency range, subjecting the coin to the first field, generating a second electromagnetic field of a substantially higher frequency range than that of the first field, subjecting the coin to the second field, producing signals indicative of the degree of interaction of the coin with each field, and producing a signal indicative of the acceptability of the coin and selective of its denomination within the set only if the degree of each interaction is within predetermined tolerances ofthose of acceptable coins of one of the denominations of the set.

2. The method of claim 1 wherein the coin is in one location when subjected to the first electromagnetic field and in a second location when subjected to the second electromagnetic field.

3. The method of claim 1 including the steps of causing the coin to move along a predetermined path with respect to the fields.

4. The method of claim 1 including the steps of sub- 5 jecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field and examining the degree of interaction of the coin with the third field wherein the acceptability signal is produced only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination.

S. The method of claim 4 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.

6. The method of claim 1 wherein the low frequency range is below approximately kHz.

7. The method of claim 1 wherein the higher frequency range is above approximately 75 kHz.

8. The method of claim 1 wherein the degree of at least one interaction is indicated by a shift in the frequency of an oscillator.

9. The method of claim 1 wherein the degree of at least one interaction is indicated by the degree of balance of a bridge circuit.

10. The method of claim 1 wherein a field of low frequency range and a field of a higher frequency range are concurrently applied to the coin.

11. The method of claim 1 including the steps of mechanically segregating acceptable coins from inacceptable coins in response to the acceptability indicative signal, producing a signal indicative of the completion of segregation of an acceptable coin, and recording the value of the coins denomination in response to the segregation signal.

12. A method for examining conductive coins with respect to authenticity and denomination comprising the steps of subjecting a coin to a first electromagnetic field of a low frequency range below 75 kHz., subjecting the coin to a second electromagnetic field of a substantially higher frequency range than that of the first field and higher than 75 kHz., producing first and second signals indicative of the degree of interaction of the first and second fields respectively with the coin, and separately examining the degree of interaction of the coin with each field and producing a signal indicative of the acceptability of the coin only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination.

13. The method, of claim 12 wherein the upper limit of the higher frequency range is lMHz.

14. The method of claim 13 wherein thelower limit of the lower frequency range is 3kHz.

15. The method of claim 12 wherein the only change in frequency of an electromagnetic field, when the coin passes through it, is coin dependent.

16. The method of claim 12 wherein the change of frequency of an electromagnetic field is detected and employed as an indicia of coin authenticity and denomination.

17. The method of claim 12 including the steps of causing the coin to move along a predetermined path with respect to the fields, subjecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field, examining the degree of interaction of the coin with the third field wherein the acceptability signal is produced only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination, and identifying the denomination of the coin.

18. The method of claim 17 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.

19. The method of claim 18 wherein the third fields frequency range is above 75kHz, the first and third fields are concurrently applied to the coin, and the coin acceptability signal is produced only if the interaction indicative signals with respect to the first and third fields are obtained concurrently.

20. The method of claim 1 wherein the first and second fields are concurrently applied to the coin, and the coin acceptability signal is produced only if the interaction indicative signals with respect to the fields are obtained concurrently. 4

21. Apparatus for examining conductive coins of a plurality of denominations with respect to authenticity and denomination within a set of acceptable coins of various denominations comprising means for subjecting a coin to a first electromagnetic field of a low frequency range, means for producing a signal indicative of the degree of interaction of the coin with the first field, separate means for subjecting the coin to a second electromagnetic field of a substantially higher frequency range than that of the first field, means for producing a signal indicative of the degree of interaction of the coin with the second field, and means for producing a signal indicative of acceptability and denomination of the coin only if both interaction indications are within predetermined tolerances of those of acceptable coins of one of the denominations of the set. 1

22. The apparatus of claim 21 wherein the means for subjecting the coin to the first field comprise a first inductorand the means for subjecting the coin to the secondfield comprise a second inductor.

23. The apparatus of claim 22 wherein the means for indicating the degree of interaction of the coin with the first field comprises a bridge circuit and the means for indicating the degree of interaction of the coin with the second field comprises frequency shift detection means. l

24. The apparatus of claim 21 wherein the low frequency range is below approximately 75 kHz.

25. The apparatus of claim 2l wherein the higher frequency range is above approximately 75 kHz.

26. The apparatus of claim 21 further comprising means for subjecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field and means for indicating the degree of interaction of the coin with the third field, wherein the acceptability signal producing means produces the acceptability signal only if all three interaction indications are within tolerances of those of acceptable coins of a given denomination.

27. The apparatus of claim 26 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.

28. The apparatus of claim 21 comprising at least one inductor operating in a higher frequency range than that of the first field for each denomination of coin to be accepted by the apparatus.

29. The apparatus of claim 21 wherein the means for producing an acceptability signal comprise digital logic circuitry having inputs connected to the outputs of at least one low frequency interaction indicating means and one high frequency interaction indicating means.

30. The apparatus of claim 21 further comprising mechanical gate means for separating acceptable coins from unacceptable coins, a coin presence sensor located in a position where it will sense accepted coins which have passed the gate and produce a signal in response thereto, and accumulator means arranged to record the value of an accepted coin in reponse to the gate passed signal.

31. Apparatus for examining conductive coins with respect to authenticity and denomination comprising a coin passageway, means for subjectinga coin in the passageway to a first electromagnetic field of alow frequency range below kl-lz., separate means for subjecting the coin to a second and a third electromagnetic field each ofa frequency range above 75 kHz. and substantially higher than that of the first field, separate means for examining the degree of interaction of each of the fields with the coin, and means for producing a signal indicative of acceptability of the coin only if each of the three interaction indications is within predetermined tolerances of those of acceptable coins of a single denomination.

32. The apparatus. of claim 31 wherein the upper limit of the higher frequency range is lMHz.

33. The apparatus of claim 32 wherein the lower limit of the lower frequency range is 3kHz. I

34. The apparatus of claim 31 wherein the degree of at least one interaction of the coin with a higher frequency field is indicated by a shift in the frequency of an oscillator and the degree of interaction of the coin with the first field is indicated by the degree of balance of a bridge circuit.

35. The apparatus of claim 31 further comprising means for causing relative motion of the coin through the fields along a predetermined path defined by a coin supporting track wherein each of the fields is produced by an inductor driven by an alternating current, and wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.

36. The apparatus of claim 35 wherein a first inductor operating in a higher frequency range than that of thefirst field and a second inductor'operating-in a low frequency range are at substantially the same longitudinal location along the coin path, and further comprising combinatorial means connected so that a signal indicative of coin acceptability is produced only if both the interaction indications with respect to said first and second inductors occur concurrently.

37. The apparatus of claim 35 further comprising at least one oscillator to-produce the alternating current, wherein at least one oscillator is connected with-its associated inductor so that the presence of conductive material in the field produced by that inductor causes the frequency of the oscillator to shift from an idling frequency.

38. The apparatus of claim 37 wherein at least one interaction examining means is a narrow band detector circuit responsive to the output signal of that oscillator for detecting a predetermined frequency shifted from the oscillators idling frequency and producing a signal indicative of the occurrence of the shifted frequency, and the detector circuit produces an output pulse for each transition of the frequency of its associated oscillator into the bandpass of the detector.

39. The apparatus of claim 35 wherein at least one of the inductors is an element of a bridge circuit, the 

1. A method for examining conductive coins with respect to both their authenticity and their denomination within a set of acceptable coins of various denominations comprising the steps of generating a first electromagnetic field of a low frequency range, subjecting the coin to the first field, generating a second electromagnetic field of a substantially higher frequency range than that of the first field, subjecting the coin to the second field, producing signals indicative of the degree of interaction of the coin with each field, and producing a signal indicative of the acceptability of the coin and selective of its denomination within the set only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of one of the denominations of the set.
 1. A method for examining conductive coins with respect to both their authenticity and their denomination within a set of acceptable coins of various denominations comprising the steps of generating a first electromagnetic field of a low frequency range, subjecting the coin to the first field, generating a second electromagnetic field of a substantially higher frequency range than that of the first field, subjecting the coin to the second field, producing signals indicative of the degree of interaction of the coin with each field, and producing a signal indicative of the acceptability of the coin and selective of its denomination within the set only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of one of the denominations of the set.
 2. The method of claim 1 wherein the coin is in one location when subjected to the first electromagnetic field and in a second location when subjected to the second electromagnetic field.
 3. The method of claim 1 including the steps of causing the coin to move along a predetermined path with respect to the fields.
 4. The method of claim 1 including the steps of subjecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field and examining the degree of interaction of the coin with the third field wherein the acceptability signal is produced only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination.
 5. The method of claim 4 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.
 6. The method of claim 1 wherein the low frequency range is below approximately 75 kHz.
 7. The method of claim 1 wherein the higher frequency range is above approximatelY 75 kHz.
 8. The method of claim 1 wherein the degree of at least one interaction is indicated by a shift in the frequency of an oscillator.
 9. The method of claim 1 wherein the degree of at least one interaction is indicated by the degree of balance of a bridge circuit.
 10. The method of claim 1 wherein a field of low frequency range and a field of a higher frequency range are concurrently applied to the coin.
 11. The method of claim 1 including the steps of mechanically segregating acceptable coins from inacceptable coins in response to the acceptability indicative signal, producing a signal indicative of the completion of segregation of an acceptable coin, and recording the value of the coin''s denomination in response to the segregation signal.
 12. A method for examining conductive coins with respect to authenticity and denomination comprising the steps of subjecting a coin to a first electromagnetic field of a low frequency range below 75 kHz., subjecting the coin to a second electromagnetic field of a substantially higher frequency range than that of the first field and higher than 75 kHz., producing first and second signals indicative of the degree of interaction of the first and second fields respectively with the coin, and separately examining the degree of interaction of the coin with each field and producing a signal indicative of the acceptability of the coin only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination.
 13. The method of claim 12 wherein the upper limit of the higher frequency range is 1MHz.
 14. The method of claim 13 wherein the lower limit of the lower frequency range is 3kHz.
 15. The method of claim 12 wherein the only change in frequency of an electromagnetic field, when the coin passes through it, is coin dependent.
 16. The method of claim 12 wherein the change of frequency of an electromagnetic field is detected and employed as an indicia of coin authenticity and denomination.
 17. The method of claim 12 including the steps of causing the coin to move along a predetermined path with respect to the fields, subjecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field, examining the degree of interaction of the coin with the third field wherein the acceptability signal is produced only if the degree of each interaction is within predetermined tolerances of those of acceptable coins of a given denomination, and identifying the denomination of the coin.
 18. The method of claim 17 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.
 19. The method of claim 18 wherein the third field''s frequency range is above 75kHz, the first and third fields are concurrently applied to the coin, and the coin acceptability signal is produced only if the interaction indicative signals with respect to the first and third fields are obtained concurrently.
 20. The method of claim 1 wherein the first and second fields are concurrently applied to the coin, and the coin acceptability signal is produced only if the interaction indicative signals with respect to the fields are obtained concurrently.
 21. Apparatus for examining conductive coins of a plurality of denominations with respect to authenticity and denomination within a set of acceptable coins of various denominations comprising means for subjecting a coin to a first electromagnetic field of a low frequency range, means for producing a signal indicative of the degree of interaction of the coin with the first field, separate means for subjecting the coin to a second electromagnetic field of a substantially higher frequency range than that of the first field, means for producing a signal indicative of the degree of interaction of the coin with the second field, and means for producing a signal indicative of acceptability and denomination of the coin only if both interaction indications are within predetermined tolerances of those of acceptable coins of one of the denominations of the set. l
 22. The apparatus of claim 21 wherein the means for subjecting the coin to the first field comprise a first inductor and the means for subjecting the coin to the second field comprise a second inductor.
 23. The apparatus of claim 22 wherein the means for indicating the degree of interaction of the coin with the first field comprises a bridge circuit and the means for indicating the degree of interaction of the coin with the second field comprises frequency shift detection means.
 24. The apparatus of claim 21 wherein the low frequency range is below approximately 75 kHz.
 25. The apparatus of claim 21 wherein the higher frequency range is above approximately 75 kHz.
 26. The apparatus of claim 21 further comprising means for subjecting the coin to a third electromagnetic field of a substantially higher frequency range than that of the first field and means for indicating the degree of interaction of the coin with the third field, wherein the acceptability signal producing means produces the acceptability signal only if all three interaction indications are within tolerances of those of acceptable coins of a given denomination.
 27. The apparatus of claim 26 wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.
 28. The apparatus of claim 21 comprising at least one inductor operating in a higher frequency range than that of the first field for each denomination of coin to be accepted by the apparatus.
 29. The apparatus of claim 21 wherein the means for producing an acceptability signal comprise digital logic circuitry having inputs connected to the outputs of at least one low frequency interaction indicating means and one high frequency interaction indicating means.
 30. The apparatus of claim 21 further comprising mechanical gate means for separating acceptable coins from unacceptable coins, a coin presence sensor located in a position where it will sense accepted coins which have passed the gate and produce a signal in response thereto, and accumulator means arranged to record the value of an accepted coin in reponse to the gate passed signal.
 31. Apparatus for examining conductive coins with respect to authenticity and denomination comprising a coin passageway, means for subjecting a coin in the passageway to a first electromagnetic field of a low frequency range below 75 kHz., separate means for subjecting the coin to a second and a third electromagnetic field each of a frequency range above 75 kHz. and substantially higher than that of the first field, separate means for examining the degree of interaction of each of the fields with the coin, and means for producing a signal indicative of acceptability of the coin only if each of the three interaction indications is within predetermined tolerances of those of acceptable coins of a single denomination.
 32. The apparatus of claim 31 wherein the upper limit of the higher frequency range is 1MHz.
 33. The apparatus of claim 32 wherein the lower limit of the lower frequency range is 3kHz.
 34. The apparatus of claim 31 wherein the degree of at least one interaction of the coin with a higher frequency field is indicated by a shift in the frequency of an oscillator and the degree of interaction of the coin with the first field is indicated by the degree of balance of a bridge circuit.
 35. The apparatus of claim 31 further comprising means for causing relative motion of the coin through the fields along a predetermined path defined by a coin supporting track wherein each of the fields is produced by an inductor driven by an alternating current, and wherein the second field is directed toward one face of the coin and the third field is directed toward the other face of the coin.
 36. The apparatus of claim 35 wherein a first inductor operating in a higher frequency range than that of the first field and a second inductor operating in a low frequency range are at substantially the same longitudinal location along the coin path, and further comprising combinatorial means connected so that a signal indicative of coin acceptability is produced only if both the interaction indications with respect to said first and second inductors occur concurrently.
 37. The apparatus of claim 35 further comprising at least one oscillator to produce the alternating current, wherein at least one oscillator is connected with its associated inductor so that the presence of conductive material in the field produced by that inductor causes the frequency of the oscillator to shift from an idling frequency.
 38. The apparatus of claim 37 wherein at least one interaction examining means is a narrow band detector circuit responsive to the output signal of that oscillator for detecting a predetermined frequency shifted from the oscillator''s idling frequency and producing a signal indicative of the occurrence of the shifted frequency, and the detector circuit produces an output pulse for each transition of the frequency of its associated oscillator into the bandpass of the detector.
 39. The apparatus of claim 35 wherein at least one of the inductors is an element of a bridge circuit, the bridge is driven by an oscillator and at least one interaction indicative means is a bridge condition detector arranged to monitor the output of the bridge.
 40. The apparatus of claim 39 wherein the detector circuit produces a single pulse each time the output of the bridge passes into and out of a range of signal values within a predetermined tolerance of a predetermined value.
 41. The apparatus of claim 39 wherein the bridge is a multileg bridge having a plurality of parallel branches in parallel with an inductor branch comprising an inductor and a resistor, and wherein each of a plurality of bridge condition detectors is connected to monitor the output of a bridge circuit comprising the inductor branch and one of the other branches.
 42. The apparatus of claim 39 wherein at least one inductor having at least one pole piece is located adjacent the coin track with at least a portion of a pole piece below the level of the track and at least a portion of a pole piece above the level of the track.
 43. The apparatus of claim 35 wherein an inductor is an element of a multileg bridge circuit having a plurality of parallel branches in parallel with an inductor branch comprising said inductor and a resistor, and wherein each of a plurality of bridge condition detectors is connected to monitor the output of a bridge circuit comprising the inductor branch and one of the other branches.
 44. The apparatus of claim 43 wherein the inductor of the inductor branch comprises a series connected pair of low frequency field producing inductors, one of which is located on each side of the coin path.
 45. The apparatus of claim 43 further comprising mechanical gate means for separating acceptable coins from unacceptable coins, a coin presence sensor located in a position where it will sense accepted coins which have passed the gate and produce a signal in response thereto, an accumulator means arranged to record the value of an accepted coin in response to the gate passed signal.
 46. Apparatus for examining conductive coins with respect to authenticity and denomination comprising first inductor means arranged to subject a face of a coin to a first electromagnetic field which would penetrate through an authentic coin of an acceptable denomination, second inductor means arranged to subject a face of the coin to a second electromagnetic field having a frequency high enough that it would not penetrate through an authentic coin of said acceptable denomination, separate means for indicating the degree of interaction of the coin with each of the fields, and means for producing a signal indicative of acceptability of the coiN as a coin of said acceptable denomination only if both interaction indications are within predetermined tolerances for acceptable coins of said denomination.
 47. The apparatus of claim 46 wherein one inductor of a series connected pair of low frequency field producing inductors is located adjacent each side of the coin path.
 48. The apparatus of claim 46 wherein a first inductor operating in a higher frequency range than that of the first field and a second inductor operating in a low frequency range are at substantially the same longitudinal location along the coin path.
 49. The apparatus of claim 48 further comprising combinatorial means connected so that a signal indicative of coin acceptability is produced only if both the interaction indications with respect to said first and second inductors occur concurrently.
 50. The apparatus of claim 46 wherein at least one inductor having at least one pole piece is located adjacent the coin track with at least a portion of a pole piece below the level of the track and at least a portion of a pole piece above the level of the track.
 51. The apparatus of claim 46 further comprising at least one oscillator to produce the alternating current, wherein at least one oscillator is connected with its associated inductor so that the presence of conductive material in the field produced by that inductor causes the frequency of the oscillator to shift from an idling frequency and at least one interaction indicating means is a narrow band detector circuit responsive to the output signal of that oscillator for detecting a predetermined frequency shifted from the oscillator''s idling frequency and producing a signal indicative of the occurrence of the shifted frequency.
 52. The apparatus of claim 51 wherein the detector circuit produces an output pulse for each transition of the frequency of its associated oscillator into the bandpass of the detector.
 53. The apparatus of claim 51 wherein the detector circuit means comprises means for periodically sampling the output signal of an associated oscillator for a predetermined sampling interval and means for producing the shifted frequency indicative signal when the number of cycles in the output signal of the oscillator circuit during each of a predetermined number of sampling intervals is substantially equal within a predetermined tolerance to a number of signal cycles predetermined for genuine coins of a denomination.
 54. The apparatus of claim 53 wherein the sampling means periodically and sequentially samples the output signals of each of a plurality of oscillator circuits.
 55. The apparatus of claim 53 wherein the means for producing an interaction indicating signal comprises a counter for counting the number of cycles in the output signal of said associated oscillator circuit during each sampling interval, a decoder signal pulse when the number of cycles counted by said first counter in any sampling interval is substantially equal to said predetermined number of signal cycles; and a second counter responsive to said decoder for producing said frequency detector output signal when the number of decoder signal pulses is substantially equal to said predetermined number of sampling intervals.
 56. The apparatus of claim 53 wherein the means for producing interaction indicating signals comprises at least one signal cycle counter responsive to said sampled oscillator output signals for producing an output signal proportional to the number of cycles in each oscillator output signal sample; and wherein the means for producing a coin acceptability indicative signal comprises at least a first and second decoder each responsive to an output signal of said signal cycle counter, each producing an output signal pulse when the number of signal cycles represented by the output signal of said signal cycle counter is substantially equal to said predetermined number of signal cycles for its associated low frequency or high frequency oscillator circuit, respectively, first and secoNd pulse counters for counting the output signal pulses produced by said first and second decoders, respectively, and logic means responsive to said first and second counters for producing a coin acceptability indicative signal when the number of output signal pulses counted by each of said pulse counters is substantially equal to said predetermined number of sampling intervals.
 57. The apparatus of claim 46 wherein at least one of the inductors if an element of a bridge circuit, the bridge is driven by the oscillator and at least one interaction indicative means is a bridge condition detector arranged to monitor the output of the bridge.
 58. The apparatus of claim 57 wherein the detector circuit produces a single pulse each time the output of the bridge passes into and out of a range of signal values within a predetermined tolerance of a predetermined value.
 59. The apparatus of claim 57 wherein the bridge is a multileg bridge having a plurality of parallel branches in parallel with an inductor branch comprising an inductor and a resistor, and wherein each of a plurality of bridge condition detectors is connected to monitor the output of a bridge circuit comprising the inductor branch and one of the other branches. 